Academia.eduAcademia.edu

Figure 3 – uploaded by Sharon Billings

See full PDFdownloadDownload figure
relationship between soil temperature and respiration at both sites in 1997, at neither site was the relationship significant at the 0.05 level. A significant positive relationship between CO, efflux and soil moisture was found in 1996 under the shelter at the floodplain and upland sites and in 1997 both outside and under the shelter at the upland site (Table 1B, P <0.05). Soil temperature was a more influential parameter on CO, efflux than soil moisture in multiple regressions of CO, efflux on soil temperature and soil moisture (Table 1C) in 1996. In 1997, neither parameter was a significant influ- ence on soil CO, efflux. upland and floodplain, season averages) were within the range of rates from other boreal forest soils, 0.16-0.46 gm-*-h'! (Gordon et al. 1987; Schlentner and Van Cleve 1985; Weber 1985). The highest rate recorded at the floodplain site, 1.45 gm-?-h!, was most likely the result of a sudden, short-term release of CO,. At the upland site, however, rates outside the shelter during 1996 were higher than previously published ranges for this area. These rates are similar to and even higher than some rates found in temperate forests (Witkamp 1969; Schlesinger 1991; Thierron and Laudelout 1996). Our flux measurements represent an integrated re- sponse of many biological and physical processes in the soil, all of which respond differently to various parameters. Thus, it is difficult to obtain a strong correlation between flux measurements and a single variable, although clearly the rainout shelters had an effect on soil surface CO, efflux (Fig. 6).

Table 1 relationship between soil temperature and respiration at both sites in 1997, at neither site was the relationship significant at the 0.05 level. A significant positive relationship between CO, efflux and soil moisture was found in 1996 under the shelter at the floodplain and upland sites and in 1997 both outside and under the shelter at the upland site (Table 1B, P <0.05). Soil temperature was a more influential parameter on CO, efflux than soil moisture in multiple regressions of CO, efflux on soil temperature and soil moisture (Table 1C) in 1996. In 1997, neither parameter was a significant influ- ence on soil CO, efflux. upland and floodplain, season averages) were within the range of rates from other boreal forest soils, 0.16-0.46 gm-*-h'! (Gordon et al. 1987; Schlentner and Van Cleve 1985; Weber 1985). The highest rate recorded at the floodplain site, 1.45 gm-?-h!, was most likely the result of a sudden, short-term release of CO,. At the upland site, however, rates outside the shelter during 1996 were higher than previously published ranges for this area. These rates are similar to and even higher than some rates found in temperate forests (Witkamp 1969; Schlesinger 1991; Thierron and Laudelout 1996). Our flux measurements represent an integrated re- sponse of many biological and physical processes in the soil, all of which respond differently to various parameters. Thus, it is difficult to obtain a strong correlation between flux measurements and a single variable, although clearly the rainout shelters had an effect on soil surface CO, efflux (Fig. 6).

Related Figures (8)

Fig. 1. Volumetric soil moisture content at 10 and 20 cm in the soil profile, upland and floodplain sites, 1996 and 1997. First data points at 20 cm at the floodplain site in 1997 are missing. The 20-cm data at the floodplain site both years show a significant difference between sheltered and unsheltered soil moisture. Differences at the upland site both years at 20 cm are not significant (a = 0.05). Data from 20 cm are emphasized in the text because most roots are concentrated in this layer of the profile. values only occurring immediately after snowmelt. Outside the shelters, the range was approximately the same, but higher values were not limited to immediately after snowmelt. types (Penman 1940; Marshall 1959; Millington and Quirk 1961; Currie 1965). We chose Marshall’s (1959) form of Fick’s Law to predict upland soil CO, fluxes, which estimates D by multiplying by an air-filled porosity term, g@°. This exponent was changed tc 1.1 to find the equation that best predicted floodplain fluxes. Air-filled porosity, @ was calculated from TDR data at 20 cm ac- cording to Vomocil (1965).
Fig. 1. Volumetric soil moisture content at 10 and 20 cm in the soil profile, upland and floodplain sites, 1996 and 1997. First data points at 20 cm at the floodplain site in 1997 are missing. The 20-cm data at the floodplain site both years show a significant difference between sheltered and unsheltered soil moisture. Differences at the upland site both years at 20 cm are not significant (a = 0.05). Data from 20 cm are emphasized in the text because most roots are concentrated in this layer of the profile. values only occurring immediately after snowmelt. Outside the shelters, the range was approximately the same, but higher values were not limited to immediately after snowmelt. types (Penman 1940; Marshall 1959; Millington and Quirk 1961; Currie 1965). We chose Marshall’s (1959) form of Fick’s Law to predict upland soil CO, fluxes, which estimates D by multiplying by an air-filled porosity term, g@°. This exponent was changed tc 1.1 to find the equation that best predicted floodplain fluxes. Air-filled porosity, @ was calculated from TDR data at 20 cm ac- cording to Vomocil (1965).
Fig. 2. Soil temperature at 20 cm in the soil profile, upland and floodplain sites, 1996 and 1997. Circles are unsheltered, control soils squares are sheltered treatment soils. P values are from a t test for equal means.
Fig. 2. Soil temperature at 20 cm in the soil profile, upland and floodplain sites, 1996 and 1997. Circles are unsheltered, control soils squares are sheltered treatment soils. P values are from a t test for equal means.
Table 1. Summary of regressions of soil CO, efflux on (A) soil temperature, (B) volumetric water content, and (C) soil profile concentrations of CO, at 20 cm, upland and floodplain sites, sheltered and unsheltered soils (dashes indicate missing data).
Table 1. Summary of regressions of soil CO, efflux on (A) soil temperature, (B) volumetric water content, and (C) soil profile concentrations of CO, at 20 cm, upland and floodplain sites, sheltered and unsheltered soils (dashes indicate missing data).
CO» concentration, winter 1996-1997, upland site
CO» concentration, winter 1996-1997, upland site
Fig. 5. CO, profile concentrations at all depths measured, floodplain site 1996 and 1997. P values are from a t test for equal means; error bars are standard errors of the means. Missing data indicate still-frozen soils, when sampling was not possible. mosphere, higher soil moisture contents partially inhibit flux of this CO, to the soil surface, resulting in higher CO, concentrations. 1996 and 1997 (P <0.05) could suggest a decrease in micro- bial activity and (or) root respiration due to moisture limita- tions. Because sheltered soils at the upland site were warmer than unsheltered soil, it is doubtful that temperature alter- ations induced by the shelter caused this decrease in CO, concentrations at 20 cm. At the floodplain site, the same pat- tern of lower CO, concentrations at 20 cm in the profile is visible in 1996 but is not significant at that site either year. Lower CO, concentrations within the soil profile at both sites may have occurred as a result of decreased throughfall, which may contain significant quantities of DOC.
Fig. 5. CO, profile concentrations at all depths measured, floodplain site 1996 and 1997. P values are from a t test for equal means; error bars are standard errors of the means. Missing data indicate still-frozen soils, when sampling was not possible. mosphere, higher soil moisture contents partially inhibit flux of this CO, to the soil surface, resulting in higher CO, concentrations. 1996 and 1997 (P <0.05) could suggest a decrease in micro- bial activity and (or) root respiration due to moisture limita- tions. Because sheltered soils at the upland site were warmer than unsheltered soil, it is doubtful that temperature alter- ations induced by the shelter caused this decrease in CO, concentrations at 20 cm. At the floodplain site, the same pat- tern of lower CO, concentrations at 20 cm in the profile is visible in 1996 but is not significant at that site either year. Lower CO, concentrations within the soil profile at both sites may have occurred as a result of decreased throughfall, which may contain significant quantities of DOC.
Fig. 6. CO, efflux rates from sheltered and unsheltered soils, upland and floodplain sites, 1996 and 1997. P values are from a t test for equal means; error bars are standard errors of the mean. When data were non-normally distributed, the Wilcoxon rank-sum test was used. Open circles indicate unsheltered soils; solid circles indicate sheltered treatment soils. tween upland soil respiration and CO, concentration at 20 cm holds true through winter months, the wintertime profile data indicate that up to 33% of the summer upland flux could occur from October to April. This corraborates well the study of Coxson and Parkinson (1987) where winter soil respiration rates were sufficiently high to account for the amount of winter itter decomposition in a Canadian aspen forest. pulses with any snow disturbance. Fluxes from soil surface also may be dissolved into melting snow (Solomon and Cerling 1987). Burton and Beauchamp’s (1994) findings of high CO, concentrations within the profile during win- ter months support our results. They reported high accumulations of CO, (up to 4000 uL-L~!) in the early win- ter during one year of their study, which corresponds to our findings.
Fig. 6. CO, efflux rates from sheltered and unsheltered soils, upland and floodplain sites, 1996 and 1997. P values are from a t test for equal means; error bars are standard errors of the mean. When data were non-normally distributed, the Wilcoxon rank-sum test was used. Open circles indicate unsheltered soils; solid circles indicate sheltered treatment soils. tween upland soil respiration and CO, concentration at 20 cm holds true through winter months, the wintertime profile data indicate that up to 33% of the summer upland flux could occur from October to April. This corraborates well the study of Coxson and Parkinson (1987) where winter soil respiration rates were sufficiently high to account for the amount of winter itter decomposition in a Canadian aspen forest. pulses with any snow disturbance. Fluxes from soil surface also may be dissolved into melting snow (Solomon and Cerling 1987). Burton and Beauchamp’s (1994) findings of high CO, concentrations within the profile during win- ter months support our results. They reported high accumulations of CO, (up to 4000 uL-L~!) in the early win- ter during one year of their study, which corresponds to our findings.
using Fick’s Law. Estimating the coefficients for D, the dif- fusion of CO, in air, is a major constraint on the accuracy of Fick’s Law. We altered the exponent on gfrom 1.5 (Mar- shall 1959) to 1.1 to empirically fit the calculated flux to measured flux. However, this ignores other significant fac- tors affecting the ability of Fick’s Law to predict soil surface gas fluxes. indicate soil-forming events in addition to biogenic pro- cesses (Burton and Beauchamp 1994). Precipitation leaching through the soil profile can serve as an agent of soil for- mation, dissolving CaCO3 and producing CO, in the process.
using Fick’s Law. Estimating the coefficients for D, the dif- fusion of CO, in air, is a major constraint on the accuracy of Fick’s Law. We altered the exponent on gfrom 1.5 (Mar- shall 1959) to 1.1 to empirically fit the calculated flux to measured flux. However, this ignores other significant fac- tors affecting the ability of Fick’s Law to predict soil surface gas fluxes. indicate soil-forming events in addition to biogenic pro- cesses (Burton and Beauchamp 1994). Precipitation leaching through the soil profile can serve as an agent of soil for- mation, dissolving CaCO3 and producing CO, in the process.
Table 2. Summary of multiple regressions of soil CO, efflux or soil temperature at 20 cm and volumetric water content at 20 cm, upland and floodplain sites, sheltered and unsheltered soils.
Table 2. Summary of multiple regressions of soil CO, efflux or soil temperature at 20 cm and volumetric water content at 20 cm, upland and floodplain sites, sheltered and unsheltered soils.
Related topics:
Earth SciencesSoil ScienceClimate ChangeClimatologyBoreal Forest
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved